This invention relates to rotary electric machines and more particularly to such machines which include a two component stator winding where variation in speed is controlled by varying the phase change of currents flowing in adjacent slots of a stator assembly.
Speed control of rotary electric machines through pole phase modulation is based on the fact that it is possible to superimpose a second magnetomotive force (MMF) pattern on a primary magnetomotive force distribution at a variable phase displacement to control the number of effective poles formed by current flow in a two component stator winding. In most respects, a polyphase induction machine may be regarded as a linear system for superimposing magnetomotive force distributions. For a particular case wherein the primary MMF is subjected to 180.degree. phase modulation or 0.degree. phase modulation, for example, by reversing one-half of a stator winding with respect to the other half, two distinct synchronous speeds are established. Machines which exhibit this type of modulation are commonly referred to as being pole amplitude modulated.
Machines in which the speed is varied by varying the phase difference between the total effective current flowing in stator winding conductors of adjacent slots are disclosed in U.S. Pat. No. 3,040,226, issued June 19, 1962 to F. C. Williams et al. The machines described in that patent exhibit continuous variation in speed which is obtained by effectively varying the number of poles generated by the stator or primary winding. This is effected by feeding current from the mains and current from at least one phase shifting device in suitable proportions to the conductors in the slots of a discontinuous primary winding, thereby effectively stretching the poles when the phase shifting device is adjusted in one direction relative to the mains current and shrinking the poles when the phase shifting device is adjusted in the other direction relative to the mains current.
A pole phase modulated machine which exhibits a number of discrete speeds within a desired range is disclosed in U.S. Pat. No. 3,161,814, issued Dec. 15, 1964 to F. C. Williams et al. That patent discloses an alternating current machine having a stator winding consisting of a slotted structure provided with a plurality of sets of coils which are so arranged that the magnetomotive force in at least some of the slots is generated by the addition of magnetomotive forces caused by current flow in the conductors of at least two sets of coils and each set of coils is so arranged that the magnitude of current flow in the conductors of the slots due to the coils of one set is a single valued function of the distance along the arc of the slotted structure occupied by the one set of coils. Switching arrangements are provided for altering the connections between coils of the different sets to enable different predetermined values of average phase difference between the currents in adjacent slots to be obtained. Both of the Williams et al patents disclose discontinuous stator winding machines. Such machines utilize arc stators which result in a reduction in power to weight ratio and are difficult to manufacture. The present invention includes a stator winding which utilizes the entire periphery for speed control applications without the necessity for large dead zones which appear in arc stator machines.